IA must not use the authority of the Buy Indian Act and the procedures contained in this part to award intergovernmental contracts to Tribal organizations to plan, operate, or administer authorized IA programs (or parts thereof) that are within the scope and intent of the Indian Self-Determination and Education Assistance Act (ISDEAA) (Pub. L. 93-638). IA must use the Buy Indian Act solely to award procurement contracts to IEEs. Contracts subject to ISDEAA must follow 25 CFR part 900.